This research project consists of clinical investigations of voice and speech characteristics in patients with Parkinson's disease before and after voice therapy. The long-range aims are to evaluate the efficacy of a model of voice treatment for these patients and generate knowledge and hypotheses regarding the physiologic and neural mechanisms underlying speech and voice changes related to treatment as well as to progression of the disease. Specific aims are (1) to evaluate the interactive roles of the respiratory and laryngeal systems in treatment-related change, (2) to document co-occurring changes in articulatory and velopharyngeal function within the context of an "increased system effort" hypothesis, (3) evaluate the relationship between treatment-related change and speech intelligibility, (4) (a) evaluate the short- and long-term effects of a model of voice therapy for patients at various stages of Parkinson's disease, (b) including a preventive program for recently diagnosed patients, (5) identify positive prognostic factors for treatment success and (6) develop a data base on the speech and voice changes accompanying progression of Parkinson's disease. The following variables will be measured before and after therapy as well as longitudinally: lung volumes, laryngeal resistance, subglottal pressure, vocal fold adduction, intensity, phonatory stability, articulatory gestures, velopharyngeal function and speech intelligibility. These investigations which address fundamental issues in voice treatment efficacy will have implications for establishing treatment models for patients with Parkinson's disease as well as for other neurolaryngeal disorders.